An energy-use analysis is presented to examine the potential energy-savings and
range-extension benefits of aerodynamic improvements to tractors and trailers
used in commercial transportation. The impetus for the study was the observation
of aerodynamically-redesigned/optimized tractor shapes of emerging zero-emission
commercial vehicles that have the potential for significant drag reduction over
conventional aerodynamic tractors.
Using wind-tunnel test results, a series of aerodynamic performance models were
developed representing a range of tractor and trailer combinations. From modern
day-cab and sleeper-cab tractors to aerodynamically-optimized zero-emission cab
concepts, paired with standard dry-van trailers or low-drag trailer concepts,
the study examines the energy use, and potential savings thereof, from
implementing various fleet configurations for different operational duty
cycles.
An energy-use analysis was implemented to estimate the energy-rate contributions
associated with inertial accelerations, grade forces, rolling resistances, and
aerodynamic-drag forces for three types of duty cycles: Long Haul, Regional
Haul, and Urban Delivery. A duty-cycle-simulation approach was implemented using
speed-dependent wind-averaged-drag models, adapted for local wind-speed
magnitudes representative of each duty-cycle environment. This method was
validated for the long-haul cycle against a constant-speed
wind-climate-simulation approach applied to a fleet-transportation network.
Results demonstrate that Urban Delivery operations expend a smaller magnitude,
and smaller relative proportion, of energy use to overcome aerodynamic drag, but
that significant savings are nonetheless possible for these operations with
aerodynamic improvements to the trucks. Over the range of tractor- and
trailer-aerodynamic improvements examined, the analyses reveal the potential for
4-27% energy-rate savings and 5-37% range extension for the Long Haul cycle,
3-16% energy-rate savings and 3-18% range extension for the Regional Haul cycle,
and with 2-9% energy-rate savings and 2-10% range extension estimated for the
Urban Delivery Cycle. Although results show significant reductions in energy use
associated with emerging zero-emission-tractor shapes, trailer-aerodynamic
improvements are shown to have about twice the potential for energy savings and
range reduction than do tractor-aerodynamic improvements.